 Welcome back to the Bioelectricity lecture series in NPTEL. So, as I told you in the beginning we have divided this course into 5 different modules and among the first modules, among all these 5 modules, the first module we introduced the course. After introducing the course I gave you a graphical representation of the different systems what will be dealing with system identification and what are the different bioelectrical phenomena, how they are being recorded and what are the advanced applications of understanding those kind of phenomena. So, after section after module 1, now we will move on to the module 2. So, just to refer back in order to keep track of the way we will be moving. So, what I did I have on my screen the first lecture where I talked about all the different kind of module. So, just look at it where we are so that we can make a move from here. So, going back to the. So, this is the part what we have already done and this is where we are going to get initiated now module 2. So, now I am moving on to the lecture 4 of the module 2. So, module 2 is under the heading of bioelectrical phenomena in animal plant sorry animal insects and fishes. So, pretty much all the animal world bioelectrical phenomena. So, the way I have divided what I will do first of all I will enumerate all the different topics I am going to deal under this and then we will pick up the first topic we will talk about and likewise we will talk about the individual topics. So, let us enumerate the topic. So, basically even before I proceed further there are at the end of the class I will tell you there are couple of a stuff which I have not really slide in properly in the 5 different modules which will come in the end to tell you which all in which module those things will get fit. But at this point for the animal kingdom bioelectrical phenomena we I have already discussed with you there are two kind of excitable or three kind of excitable cells in the body which has the potential to produce action potential. So, one of them is nerve cell which constitute the complete nervous mechanism of the body a nervous system of the body. The second one is the cardiac system which ensures that our heart beats at a specific pace in a specific manner and pumps the plot all over the body. And the third section is the muscle of the skeletal muscle and the smooth muscle which ensures that either in the gut the food moves through the GI tract properly that is the function of the smooth muscle and the skeletal muscle which ensures all our physical movement mechanical movement which are of course driven by the nervous system. So, under these three classes we are going to study the animal kingdom electricity and initial phase what we will do is that we will be referring most of the time in the beginning with the nerve cells. So, let us enumerate all the different topics we are going to deal in this section. So, back here so we are into module 2 module 2 is essentially your bioelectrical phenomenon in fishes and insects. So, this is the broad title of this module under which we will be studying bioelectric potentials that is the first topic stepping stone into this world bioelectric potentials. And of course, we will be referring to the nerve cells for that talking about the ion channels I have briefly told you about the different kind of ion channels which are present third topic will be action potentials again we will be referring mostly to the nervous system talking about some of the techniques here which will come into play without these techniques the kind of immaterial. So, here I will just interrupt. So, essentially the reason why to push the technique here itself some of the techniques because without realizing the technique without appreciating the technique it is really it becomes really drab to see how those different potentials are being measured how those different current are being measured out the current flux is being determined. So, that is why I have introduced part of the instrumentation here, but again in the instrumentation section we will kind of cover those parts which I cannot cover here under the broad spectrum and that will shorten and so that we can devote little bit more time on these sections as well as it will cut short some of the classes on that section. So, that way we can adjust everything. So, voltage clamp studies then talking about the current clamp current clamp studies and then you have capacitance measurement and the significance will come. So, capacitance measurement followed by impulse propagation then we have in that same line we could introduce the brain and the memory this is we will get an opportunity to introduce the brain chip and all those things sensory circuits and special senses. So, all these nine topics what I have just now talked about all these nine topics will be essentially will be dealing with the nerve using nerve as a model system apart from here this zone out here we can talk about the two one it will be in the actually the three one in the nerves skeletal muscle action potential and cardiac muscle. We can talk this because already we have talked about the ion channels and as tenth topic what I will be dealing here will be your muscular junction 11th one will be of course they will be going hand in hand actually skeletal muscle skeletal muscle electricity mechanical action and in the same line we will have the cardiac electrophysiology. So, this is where you see the cardiac comes into play and this is where the nerve and muscle will come into play. So, this is the overall layout of the section two or the module two of this course. So, to start off so if you go back to so we will be starting with this part bioelectric potentials. So, let us get back to the bioelectric potentials what bioelectric potentials are and why how they arise to start it first. So, talking about bioelectric potentials there is always a flow of energy from higher potential to lower potential this much you all know say something is at higher potential some if water is stored at higher altitude lower altitude they will try to move and they will try to you know balance it out. So, potential is essentially word of difference of energy of two systems. So, any kind of flow of energy will take place when there is a potential difference without potential difference there cannot be any flow of information from one system to another it is that very important. And as a matter of fact the biological systems which have evolved they have evolved it is believed they have evolved from sea which is rich in sodium chloride and all these kind of things. And the way the first cell was formed it is believed somewhere or other from that harsh environment of the sea a confined structure was formed which ensures that the sodium concentration inside that confined structure is significantly low and there should be a way to pump out the excess sodium. So, that life can evolve because at a very very high salt concentration it is really challenging for life to evolve not very many life can evolve. So, it is being believed that the first cell which has formed has evolved from water and the first membrane the story is very murky out there nobody can really see with 100 percent guarantee that this is how the first membrane was formed. But what we know for sure is there is a membrane all over the biological system there are membranes all over biological systems and these membranes are semi permeable in nature and they are made up of a bilipid layer you can refer to some of the books which I will recommend you at the end of the class which will help you to brush your basics you can go through striers biochemistry you can go through leningers biochemistry which will help you to understand the bilipid structure of the membrane I will briefly deal with it, but again all the different kind of lipids which are involved in it and all those other finer details you kindly need to look into it or you can refer to the course in physiology where you will see how the first membrane has evolved and what are the different components of it. So, coming back to it somewhere or other the when the first enclose a structure which evolved it ensured that that structure had lower sodium concentration. So, in other word if I graphically show it to you. So, for example, so imagine this is the water from where life is evolving. So, now when the first cell must have evolved at some distant past or somewhere at some point. So, this is extremely high in sodium and chloride exceptionally high. When the first cell must have evolved it must have taken a very different kind of route while it has self assembled to form a enclose a structure it ensured that inside the enclose a structure the ionic concentration of sodium is low. So, inside this as well as chloride is low first evolving cell. Now, when the when now you have a enclose a structure whose sodium is low and chloride is low and if somewhere or other you have a mechanism by which this membrane can ensure that it can get rid of the sodium and always maintain a lower concentration from the surrounding. Then it can lead to a generation of bioelectric potential. So, for example, what I mean by that is. So, for example, I have a mechanism by which I ensure that you know I ensure that you know different kind of gates. So, these are the different kind of ionic gates and these ionic gates ensuring that low sodium and chloride level is maintained inside the cell. If one can do this kind of situation if somewhere or other you have these ionic gates which ensures that the sodium and chloride inside is maintained at a lower concentration as compared to the concentration of sodium and chloride which is outside into the system. Then we are talking about generating the first bioelectric potential and these kind of membranes are termed as a technical term for this kind of membranes. These are called semi permeable membrane and they are semi permeable membrane and these membranes are asymmetric in nature is the first thing they have. Then they have selective gating of ion potential for actually the word potential for selective gatings of ions and which is being regulated essentially by this ionic gates which in the modern world we call them as which will be our next topic actually will be ion channels and it has a semi permeable membrane. So, as soon as you have say for example, the word is coming back. So, say for example, if this is the cell what we just now kind of develop and say for example, sodium has say 10 molecules inside chloride has 10 molecules inside and sodium outside has 100 molecules and chloride outside has 100 molecules. So, what essentially we are doing across this like this across this what we are showing there is a potential difference and this potential difference could be represented by delta V or V is the voltage will come into all these details and what essentially will happen in a normal condition if this membrane is non-selective it allows the free diffusion to take place. If the free diffusion happens and what we will get out here is after a point of time. So, if you add up this 100 plus 110 100 plus 10 makes 110 and same way for chloride 100 plus 10 110 divided by 2 divided by 2. So, eventually there will be a time come and it will become 55 55 for sodium and for chloride 55 55 for chloride eventually. If free diffusion is permitted, but biology is smart when the first membrane of what I told you in the just the previous slide it is asymmetric. In other word what does that mean is if you go back where I showed you this word when I used this critical word it is asymmetric and it exhibit differential gating differential of ions in either direction in either direction. What does that essentially means that means this membrane which is present may allow the sodium to get in or allow the sodium to move out or allow the chloride to move in or move out it can only do that particular gate can only open in one direction. In other word if this is the gate say for example, I take example of this gate this is the gate out here in red these this gate may either allow sodium to get in, but this very same gate this very same gate is not going to allow sodium to go out mind it. So, it is in essentially this is what means just trying to explain you that it exhibit differential movement of ion in either direction or say for example, this gate if it allows chloride to move out it will not allow chloride to move in these are some of the very very fundamental concept with needed to be gras before we understand the animal kingdom by electricity and this will be dealing with in the next section next class in ion channels, but before that. So, this is essentially is where potential difference is being created and this potential difference is being maintained all throughout our life because there are channels all over the place which will not allow the ions to move freely they are being regulated they are being governed and flow of ion is being is a function which will be coming the next to next class where we will be talking about there are two counter forces which are functioning here one is of course, your force of diffusion this is force one and there is another force two which is the charge within the electrolytes and here the electrolytes are could be sodium could be chloride could be potassium could be magnesium could be even proteins because they also have whole lot of charge in them the summation there they have summated charges on them oh apart from it here which you forgot is calcium and yeah mostly calcium sodium magnesium sodium chloride magnesium proteins here likewise. So, there are whole range of electrolytes which are present and apart from it there are few non electrolytes their diffusion is totally different we are not going to deal at this time how they are diffusing I will briefly touch upon it while I will be talking about the nurse equation and the balancing act here between these two forces you look at this force one and force two free diffusion force and the charge within the electrolyte the balancing act is driven by nurse or nurse equilibrium. So, I will devote at least half a class on this nurse equilibrium before I move on to the ion channels at this point what I wanted to highlight is these ions can move freely from this side to this side if only diffusion is allowed. So, that would not allow us to maintain a membrane potential, but yet there is a membrane potential. So, if you look at it if we just to give you an idea about the membrane potentials which are present. So, those of you are exposed to say for examples and I will be taking the example of a neuron. So, this is the neuron which is sitting this is the cell body these are the dendrites this is the axon this is the cell body this is the nucleus and these are the dendrites. So, if you impel an electrode here like this and measure the potential with respect to outside you will find that this electrode and you are actually here what you are essentially doing you are measuring potential across difference delta v and this is the neuron. So, what will you essentially your recording will tell you will see approximately minus 70 millivolt sometime it may go out all the way up to minus 80 millivolt. In other word whenever we talk about membrane potential of the electron what we are talking about is that with respect to outside the inside is more negative. So, essentially what does that mean is here it is more negative with respect to the outside just bear with it because I am just going out, but that essentially means is that these are positive with respect to the outside. Whereas, inside it is these are all negative negative negative. So, with respect to the outside inside is more negative why is it more negative now what we will do over last 100 years all the different concentrations of the electrolytes which have been discovered we will I will give you the complete list of it that will give you an idea why with respect to inside the outside is more positive or with with respect to outside inside is more negative. So, what will essentially do here we will talk about the extracellular concentration of the two different two major cells especially we will take about muscle or frog we will take the nerve which is another. So, these two nerve of squid we will talk little bit more about a squid once I am done with this these are the two systems we will be looking at and what we will be looking at here will be the intracellular I am coming to this intracellular in millimolar. So, I think I will just take here let me do it like this intracellular millimolar and extracellular millimolar. So, if you go back to the diagram what I was drawing free people. So, out here this is intracellular that is inside the cell this is all extracellular which is outside the cell. So, coming back the intracellular and extracellular and here we are enumerating the different ions or electrolytes we are talking about all right and these are the anions which could be protein or whatsoever. So, in case of muscle it is 124 millimolar intracellular 4 millimolar intracellular sodium chloride is 1.5 millimolar and other anions 126.5 whereas, in the extracellular potassium is exceptionally low if you compare these two values out here look at the two values compare the two values you will see potassium is very low outside whereas, sodium if you look at sodium it goes up out here it is almost 109.0 whereas, chloride is very high outside 77.0 and there are no anion outside because all the proteins are inside the cell. Now, talking about the nerves if you look at the nerves now again the same way we are dividing intracellular in terms of millimolar extracellular in terms of millimolar. So, for potassium intracellular potassium is 397 millimolar whereas, it is 20 millimolar in extracellular. So, essentially there is of the direction is something like this whereas, out here it was direction was just here the same out here also whereas, in terms of potassium sorry in terms of sodium is 15 intracellular and 437 extracellular very high chloride is 40 intracellular and 556 extracellular. And most of this extracellular is with respect pretty much you can they are comparable with seawater and that is one of the clues which says that life is evolved from sea life is evolved from water. So, all these values what you see 2.2 109 and all this. So, just let me go back to the slides just kind of highlight that. So, if you compare these values which I am putting in green now here or so all these values are kind of similar to the seawater. And now if I go back to the slide which I wanted to show you in the whichever showing in the beginning in the first slide out here. So, essentially this was I was trying to explain in the first slide to start off with that if sodium and in chloride is low out inside whereas, sodium and chloride is high outside. And we found out that potassium is low. So, I am adding on this diagram potassium is high inside and there are lot of proteins which you say a negative inside it which we call as a negative or the anions which are present there which are jointly represented as all the proteins. So, now the challenge for biology comes how it maintains this potential so neatly over a period of time and how that is getting regulated. So, coming back to where I was yeah. So, this is the concentration which is currently accepted and there may be few number here and there which varies. So, from here we will take two parts what we will do in the next class and from here we will derive the Nernst equation we will talk about how the Nernst equation regulates. So, if you look at this picture itself that will tell you the whole story. So, look at this picture you see these are the electrolytes which are present out here. So, if I draw this in terms of just for your visualization sake if this is the cell and you have sodium which is very high chloride very high potassium very low potassium very high chloride low sodium low and you have an anion in terms of proteins which is very high. Now, going by the simple diffusion you can appreciate it here going by the simple diffusion what will happen if I take case by case these should if going by pure diffusion these should become equal. Similarly, if I take these two chloride and this chloride should become equal similarly potassium and potassium will become equal and part of this protein will move out like this to outside to make a new concentration a negative a negative equal this is the pure diffusion a hypothetical situation this is basically a hypothetical situation for your understanding sake. This is a pure diffusion a pure diffusion is allowed that is what is going to happen, but I put an condition here condition which I put is that those huge proteins which are present inside the cell cannot really move out. So, essentially what I am trying to tell you now this transfer or this transfer is not allowed first not allowed. So, the very moment I say I would not allow one of the component out of the four not to come out. So, automatically the charge inside it is now confined more charge. So, whenever there is a more charge inside it generates a potential around that small confined area except it now comes I say I start I am not starting putting conditions I am putting like you know I am questions right what should be I am introducing limitations on the flow of electrolyte. Now, I put the next limitation the next limitation is this this particular thing that sodium can only move from here to here through the sodium channel second limitations I put. Third limitations I put is this one this potassium can only move out like this. So, I am just putting limitations after limitations into the game I am not doing anything I am just putting limitations. So, in the light of these limitations we will be talking about two aspects what we will be going to talk about one will be ok. So, this is the pure hypothetical pure diffusion situation I give you another situation in that same line another hypothetical situation charge equilibrium. In other word what I am essentially trying to tell you is that if I am not allowing this process to take place a negatives cannot go out. Then I have to ensure in the first place the charge or the positive or the negative charge generated by sodium or chloride respectively and the potassium and few other ions which are present like calcium I have not talked about the calcium. So, you have the calcium also here which are which is contributing to positive charges out there. So, the charge has to be equilibrated on both sides. So, we have two opposing or two forces which are governing which I just mentioned in the previous if I go back to my one of my previous slides or I was telling you yes. So, this is what essentially I was trying to highlight diffusion charge and that is the stage where I will be introducing you to the these two forces in the light of these values now since you know these values will introduce Nernst which is discovered by Walter Nernst and the earlier half of the last century somewhere around 1900. So, at this point what I will do I am not introducing Nernst immediately I will highlight or I will take your attention to another aspect of electricity which will be helpful for your understanding whenever you were being taught electricity we talked about you know along a conductor if you look back. So, we always say if this is a conductor through which charge is flowing you always say there is electron which are in motion. So, those are electron mobility which governs your electrical phenomena this is what we are always exposed to, but simultaneously say for example along a channel you have ions moving along the gradient these are called ionic movement or ionic charge movement and ionic charge movement is also an electricity. So, in other word in the light of this slide I am dividing electricity into two parts one is ionic electricity and the other one is electron electricity and in biological system both these phenomena are being seen it is not that we only see one phenomena. So, what I will do just with this brief introduction I will just highlight some of the areas where we will be talking about electron and some of the areas will be talking about ion and some of the areas will be talking about the interface of the ions and the electrons. So, let us see where all we see ionic electricity sorry electron based let us say electron mobility in biological system the classic example is photosynthesis where basically when a light falls h nu when the light falls it from the chlorophyll molecule electron is actually ejected out. So, we essentially see a electron movement and second place where we see is mitochondria and as a matter of the whole term is electron transport chain. So, these are the two example and will come many more such examples where we will see electron transport and as we will be studying about all these things in the photosynthetic biology we will talk about it apart from it talking about ionic charge electricity out here this is seen all over the place in the nerve impulse in the nerve cardiac system in the muscle in neuromuscular junction I am just putting at NMJ. So, all over the place you see ionic charge mobility. So, these are the two forms of electricity which will be dealing continuously there will be interplay of electron as well as ion and this is what I wanted to highlight that as I will proceed through please brush up some of the basics especially. So, I have introduced you to this. So, please brush up the most central law into the game V is equal to I R which is basically the ohm's law where V is your voltage and I is the current and R is the resistance these are some of the basics which will be extremely essential and go through the simple series circuit and the parallel circuit wherever needed I will just introduce them wherever it will be essential. But, I just expect you people to kind of brush all these basics because that will help you to appreciate some of these things much better as compared to just mean very briefly touching up on and going to the phenomenon. So, this is what I expect you people to kind of go through some of the fundamentals. So, coming back where we were with the bio electric potential. So, these potentials as I told you that and next we will be talking about the nurse equation how these are being covered and then what we will do we will move on to the membrane structure to introduce you to the ion channels exactly these ion channels are gated. So, I should I told you they are asymmetric they open only in one direction either they will ensure an a specific ion to move out or they won't they will allow it to move in and this is further they are opening and closing is further regulated by the voltage across the membrane as you remember while I was drawing if you see this picture. So, I told you that across this there is a so essentially there is a potential difference out here delta v and the change in this change in v leads to opening and closing of ion channels. In other word this gives rise to something called v g or voltage gated ion conducting channel or ion channels where voltage is ensuring a change a delta v out here is ensuring whether the channel will be in a open state or will be in a closed state and these are all pico nano femtosecond phenomena they are very very intense phenomena which takes place in a split of the moment and which pretty much regulates or ensure that we are kicking alive and kicking. So, with this brief background of bioelectric potential I will close on this class and I told a promise to that I will plug it plug in some of the things which I missed upon. So, some of the things which I missed in the first lecture which I will just come back yeah. So, what where I am going to so I told you that I will be talking about these inanimate objects of biological origin and their electrical phenomena which in the second lecture I was telling of the thermal regulation all those things. So, what I decided is this since it is not exclusively mentioned here what we will I will do is I will include them in this section out here in the bio energy section. So, basically out here we will talk about inanimate object of bio origin and electrical event. So, that is why we will be talking about T e or thermoelectric events and out here in the bio electricity of plants and all these things will introduce actually the photosynthesis. These are the two things which were sorry there is one more thing which is and in this section itself we will introduce this some of these insect based solar cell I told you solar cell this is why these are the three things which were not very clearly was coming out while I was kind of highlighting the course that where those will fit. So, those will fit as under the bio energy section where we will deal with those things. So, I will close on this and in the next class we will talk about the Nernst equation and we will talk about the action potential followed by that and in well we will sorry we will be talking about the ion channels and then the action potentials and in the in between this we will slide in the exact picture of the membrane how it looks like and how the ion channels three dimensional geometries are. So, thanks a lot.